WEBVTT

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I am holding something remarkably old.

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It is older than any human artifact,

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older than life on Earth,

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older than the continents
and the oceans between them.

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This was formed
over four billion years ago

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in the earliest days of the solar system

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while the planets were still forming.

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This rusty lump of nickel and iron
may not appear special,

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but when it is cut open ...

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you can see that it is different
from earthly metals.

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This pattern reveals metallic crystals
that can only form out in space

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where molten metal
can cool extremely slowly,

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a few degrees every million years.

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This was once part
of a much larger object,

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one of millions left over
after the planets formed.

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We call these objects asteroids.

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Asteroids are our oldest
and most numerous cosmic neighbors.

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This graphic shows near-Earth asteroids
orbiting around the Sun,

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shown in yellow,

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and swinging close to the Earth's orbit,

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shown in blue.

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The sizes of the Earth, Sun and asteroids
have been greatly exaggerated

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so you can see them clearly.

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Teams of scientists across the globe
are searching for these objects,

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discovering new ones every day,

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steadily mapping near-Earth space.

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Much of this work is funded by NASA.

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I think of the search for these asteroids
as a giant public works project,

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but instead of building a highway,
we're charting outer space,

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building an archive
that will last for generations.

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These are the 1,556 near-Earth asteroids
discovered just last year.

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And these are all of the known
near-Earth asteroids,

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which at last count was 13,733.

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Each one has been imaged, cataloged

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and had its path
around the Sun determined.

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Although it varies
from asteroid to asteroid,

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the paths of most asteroids
can be predicted for dozens of years.

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And the paths of some asteroids can be
predicted with incredible precision.

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For example, scientists
at the Jet Propulsion Laboratory

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predicted where the asteroid Toutatis
was going to be four years in advance

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to within 30 kilometers.

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In those four years,

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Toutatis traveled 8.5 billion kilometers.

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That's a fractional precision

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of 0.000000004.

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(Laughter)

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Now, the reason I have
this beautiful asteroid fragment

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is because, like all neighbors,

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asteroids sometimes drop by unexpectedly.

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(Laughter)

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Three years ago today,

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a small asteroid exploded
over the city of Chelyabinsk, Russia.

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That object was about 19 meters across,

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or about as big as a convenience store.

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Objects of this size hit the Earth
every 50 years or so.

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66 million years ago,

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a much larger object hit the Earth,

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causing a massive extinction.

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75 percent of plant
and animal species were lost,

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including, sadly, the dinosaurs.

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That object was
about 10 kilometers across,

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and 10 kilometers is roughly
the cruising altitude of a 747 jet.

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So the next time you're in an airplane,

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snag a window seat, look out
and imagine a rock so enormous

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that resting on the ground,

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it just grazes your wingtip.

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It's so wide that it takes your plane
one full minute to fly past it.

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That's the size of the asteroid
that hit the Earth.

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It has only been within my lifetime

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that asteroids have been considered
a credible threat to our planet.

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And since then, there's been
a focused effort underway

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to discover and catalog these objects.

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I am lucky enough
to be part of this effort.

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I'm part of a team of scientists
that use NASA's NEOWISE telescope.

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Now, NEOWISE was not
designed to find asteroids.

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It was designed to orbit the earth
and look far beyond our solar system

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to seek out the coldest stars
and the most luminous galaxies.

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And it did that very well
for its designed lifetime of seven months.

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But today, six years later,
it's still going.

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We've repurposed it
to discover and study asteroids.

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And although it's
a wonderful little space robot,

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these days it's kind of like a used car.

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The cryogen that used to refrigerate
its sensors is long gone,

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so we joke that
its air-conditioning is broken.

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It's got 920 million miles
on the odometer,

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but it still runs great

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and reliably takes a photograph
of the sky every 11 seconds.

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It's taken 23 photos
since I began speaking to you.

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One of the reasons NEOWISE is so valuable

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is that it sees the sky
in the thermal infrared.

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That means that instead of seeing
the sunlight that asteroids reflect,

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NEOWISE sees the heat that they emit.

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This is a vital capability
since some asteroids are as dark as coal

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and can be difficult or impossible
to spot with other telescopes.

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But all asteroids, light or dark,
shine brightly for NEOWISE.

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Astronomers are using
every technique at their disposal

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to discover and study asteroids.

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In 2010, a historic milestone was reached.

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The community, together, discovered
over 90 percent of asteroids

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bigger than one kilometer across --

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objects capable
of massive destruction to Earth.

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But the job's not done yet.

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An object 140 meters or bigger
could decimate a medium-sized country.

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So far, we've only found
25 percent of those.

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We must keep searching the sky
for near-Earth asteroids.

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We are the only species
able to understand calculus

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or build telescopes.

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We know how to find these objects.

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This is our responsibility.

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If we found a hazardous asteroid
with significant early warning,

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we could nudge it out of the way.

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Unlike earthquakes, hurricanes
or volcanic eruptions,

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an asteroid impact
can be precisely predicted

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and prevented.

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What we need to do now
is map near-Earth space.

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We must keep searching the sky.

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Thank you.

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(Applause)